The present invention relates to a method for the fabrication of an electrostatic microswitch, and more particularly to a method for fabricating an electrostatic microswitch which can improve on the downward deflection problem of the formed microbeam.
Micromechanical structures, including polysilicon beams, have been used in a variety of mechanical devices, such as resonant sensors, electrostatic micromotors, etc. For example, the literature, M. W. Putty et al., "Process Integration for Active Polysilicon Resonant Microstructures", Sensors and Actuators, 20 (1988), pp. 143-151, discusses the processing issues for integrating electrostatically-driven and -sensed polysilicon resonant microstructures with on-chip nMOS devices. Surface-micromachining using sacrificial spacer layers is utilized to obtain released resonant microstructures. Its novel feature is the use of rapid thermal annealing (RTA) for strain relief of the ion-implanted, phosphorous-doped polysilicon microstructure. The literature of R. S. Muller, "Microdynamics", Sensors and Actuators, A21-A23 (1990), pp. 1-8, discusses the possible fabrication of a new class of microdynamic mechanisms, including polysilicon resonant beams, microvalves, micromotors, microfabricated resonant structures, etc., through the exploitation of technologies based upon the IC (integrated-circuit) microfabrication process. The literature of C. Linder and N. F. de Rooij, "Investigations on Free-standing Polysilicon Beams in View of their Application as Transducers", Sensors and Actuators, A21-A23 (1990), pp. 1053-1059, discusses the fabrication and comparison of different polysilicon beams. Undoped and phosphorus-doped (P-doped) sacrificial silicon dioxide/polysilicon beam material combinations are investigated. It is concluded that the maximum flee-standing beam length is larger for the P-doped than for the undoped polysilicon beams.
It has been discussed that the key processing steps for fabricating high performance micromechanical devices are the patterning of the fine polysilicon microstructure and the lateral etching of the sacrificial layer. The present invention mainly proposes a novel polysilicon beam structure and its fabrication process in order to accomplish a high performance electrostatic microswitch.